Not applicable
The present invention relates generally to the field of continuous high tensile modulus fibers and more particularly to a method and apparatus for removing broken filaments from fiber tows.
It is common today to use carbon fiber formed from polyacrylonitrile in a continuous fiber tow or bundle form in applications such as prepegging, filament winding and pultrusion, where high tensile modulus fibers are desired. In these applications it is frequently important that the tow have a very low content of broken filaments. Broken filaments are exhibited as a readily visible fuzz that protrudes from the surface of the fiber bundle. Unacceptable amounts of fuzz lead to a variety of problems for the end-user, such as airborne fly, restriction of processing guides, imperfections in the surface of the finished product and in some cases degradation in the mechanical performance of the finished product.
Within the carbon fiber industry it is typical to measure the fuzz content in terms of the weight of fuzz removable from a specific length of tow by a recognized test procedure in which the tow is passed between two surfaces, at least one of which is a stationary foam pad capable of capturing the broken filaments while leaving the continuous fibers intact. In many applications, acceptable levels of fuzz should be less than 30 mg of fuzz per 150 feet of tow for tows with filament counts above 25,000. However, given the current qualities of polyacrylonitrile, carbon fiber tows manufactured therefrom have typical fuzz levels exceeding 50 mg per 150 feet of tow.
Accordingly, it is an object of the present invention to provide a method and apparatus for removing broken filaments from a carbon fiber tow.
It is also an object to provide a method and apparatus for reducing the fuzz level in a carbon fiber tow.
It is a further object to provide a method and apparatus for continuously removing broken filaments from a continuous carbon fiber tow.
These and other objects of the present invention will become apparent upon a consideration of the drawings referred to hereinafter and a complete description thereof.
In accordance with the present invention, as a tow moves from a station at which sizing is applied and dried to a collection station, the tow frictionally engages a rotating roller oriented in a position such that the axis of rotation is generally perpendicular to the direction of motion of the tow. The sizing may comprise an epoxy, other thermosets, such as phenolic, polyurethanes, vinylesters or polyesters, or thermoplastics, such as polyurethanes, polypropylene, polyamide or polyester. The roller rotates in a direction opposite to the direction of movement of the tow at the point of frictional engagement. The exterior surface of the roller is covered with a rubber material adapted to engage broken ends of fibers and direct those broken fibers to a vacuum nozzle located adjacent to the roller for collection of the broken fibers in a vacuum canister. The use of vacuum alone is not sufficient to remove broken filaments.